1. Field of the Invention
The present invention relates to an apparatus and method for eliminating noise contained within a usable frequency band of a mobile communication terminal, and more particularly, to an apparatus and method for eliminating a multiplication signal of a transmission signal, which is recognized as noise when it exists within a usable frequency band of a wireless communication.
2. Description of the Related Art
The use of mobile communication terminals is rapidly increasing because they are handy to carry. With the increasing use of mobile communication terminals, service providers (terminal manufacturers) have made efforts to provide a more stable and reliable call quality and to provide a variety of services so as to attract many users.
In the communication service fields, the elimination of noise from the transmitted or received signals has been studied so as to provide reliable services.
FIG. 1 is a block diagram illustrating transmission of data and control signals between modules in a conventional mobile communication terminal. In a mobile communication terminal shown in FIG. 1, data and control signals are transmitted and received between a Central Processing Unit (CPU) 101 and a peripheral device (for example, a Liquid Crystal Display (LCD) or a camera module) 103 at a constant transfer rate. A transmission waveform of the data and control signals is generally a square wave. Because the square wave consists of a sum of sine waves, there exists harmonic components (hereinafter, referred to as multiplication signals) that are integer multiples of the fundamental frequency.
For example, the mobile communication terminal generally uses a 19.2 MHz main clock. In data transmission, the mobile communication terminal uses 16-stage buses and transmits 2-3 MHz data for one bus. Therefore, harmonics that are integer multiples of the transmission speed are caused.
When the multiplication signals caused by the transmission signal exist within a usable frequency band of the wireless communication, the mobile communication terminal recognizes them as noise.
For example, a frequency band of 869-894 MHz is usable in a Code Division Multiple Access (CDMA) system. Assuming that a transmission speed inside of the mobile communication terminal is 3 MHz during CDMA communication, harmonics that are integer multiples of 3 MHz exist in the communication terminal and the multiplication signals of the transmission signal are contained within the useable frequency band of the CDMA system. Therefore, the mobile communication terminal recognizes the multiplication signals contained within the usable frequency band as noise.
As described above, when the multiplication signals according to the transmission speed inside of the mobile communication terminal exist within the usable frequency band during wireless communication, the mobile communication terminal recognizes the received signal containing the multiplication signals as noise, resulting in degradation in the reception performance of the mobile communication terminal.